Since the introduction of event related potentials (ERPs) in developmental research, a great deal has been learned about the sensory and cognitive neurophysiologic processes of the non-verbal infant. The use of this non-invasive measure has informed us about early socio- emotional skills from infants' abilities to discriminate emotion expressions to their memory for faces and imitated acts. Although one can argue that seeing an angry or fearful face induces a certain amount of stress, the primary intention of this previous research has not been to evaluate infants' reactions to or memory of social stress. This gap in the literature exists even though there have been rapid advancements in our understanding of infant social capacities and their reactions to social stress. The proposed project aims to develop an ERP paradigm to examine infants' response to and memory of a socially stressful interaction, the Face-to-Face Still Face (FFSF) paradigm. This proposal will make a significant contribution to the field because it serves as a first step in addressing the gap in the literature by exploring the neurophysiologic indices of infants' memory of everyday social stress. Ultimately this paradigm and the data generated by this R21 will be used to propose a R01. One of the primary methodological issues to overcome in integrating these two experimental approaches is that ERPs studies require a large number of short, discrete trials in order to isolate important neural responses from artifacts in the EEG signal. The FFSF paradigm, however, is a live, continuous interaction between the mother and her infant. These differences make bringing both paradigms together challenging. In the initial paradigm, infants will be separated into an experimental or a control typical-play group. The experimental group will be exposed to the FFSF paradigm. The next day infants will participate in an ERP task. We will examine ERP components and we hypothesize that there will be differences between the two groups if infants in the experimental group remember the social stressor. The uniqueness of this project allows for exploratory questions to be asked of the ERP data. Specifically we will address what currently is unclear, the impact of the interactive social stressor as seen in the ERP waveform. Developing this measure will be of significance for understanding how stressful experiences are memorialized early in development and will provide a paradigm for evaluating the long- term impact of stressors on the developing social brain and on typical and atypical development, a significant goal of the NIH mission.